Systems and methods for intelligent control related to TRIAC dimmers

ABSTRACT

System controller and method for a lighting system. The system controller includes a first controller terminal configured to receive a first signal, and a second controller terminal configured to output a second signal to a diver component. The driver component is configured to receive a first current and provide one or more drive currents to one or more light emitting diodes in response to the second signal. Additionally, the system controller is configured to process information associated with the first signal, determine a first time period for the first signal to increase from a first threshold to a second threshold, and determine a second time period for the first signal to decrease from the second threshold to the first threshold.

1. CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to Chinese Patent Application No. 201410172086.6, filed Apr. 25, 2014, commonly assigned, incorporated by reference herein for all purposes.

Additionally, this application is related to U.S. patent application Ser. No. 14/451,656, which is incorporated by reference herein for all purposes.

2. BACKGROUND OF THE INVENTION

Certain embodiments of the present invention are directed to integrated circuits. More particularly, some embodiments of the invention provide a system and method for intelligent control related to TRIAC dimmers. Merely by way of example, some embodiments of the invention have been applied to driving light emitting diodes (LEDs). But it would be recognized that the invention has a much broader range of applicability.

A conventional lighting system may include or may not include a TRIAC dimmer that is a dimmer including a Triode for Alternating Current (TRIAC). For example, the TRIAC dimmer is either a leading-edge TRIAC dimmer or a trailing-edge TRIAC dimmer. Often, the leading-edge TRIAC dimmer and the trailing-edge TRIAC dimmer are configured to receive an alternating-current (AC) input voltage, process the AC input voltage by clipping part of the waveform of the AC input voltage, and generate an voltage that is then received by a rectifier (e.g., a full wave rectifying bridge) in order to generate a rectified output voltage.

FIG. 1 shows certain conventional timing diagrams for a leading-edge TRIAC dimmer and a trailing-edge TRIAC dimmer. The waveforms 110, 120, and 130 are merely examples. Each of the waveforms 110, 120, and 130 represents a rectified output voltage as a function of time that is generated by a rectifier. For the waveform 110, the rectifier receives an AC input voltage without any processing by a TRIAC dimmer. For the waveform 120, an AC input voltage is received by a leading-edge TRIAC dimmer, and the voltage generated by the leading-edge TRIAC dimmer is received by the rectifier, which then generates the rectified output voltage. For the waveform 130, an AC input voltage is received by a trailing-edge TRIAC dimmer, and the voltage generated by the trailing-edge TRIAC dimmer is received by the rectifier, which then generates the rectified output voltage.

As shown by the waveform 110, each cycle of the rectified output voltage has, for example, a phase angel (e.g., φ) that changes from 0° to 180° and then from 180° to 360°. As shown by the waveform 120, the leading-edge TRIAC dimmer usually processes the AC input voltage by clipping part of the waveform that corresponds to the phase angel starting at 0° or starting at 180°. As shown by the waveform 130, the trailing-edge TRIAC dimmer often processes the AC input voltage by clipping part of the waveform that corresponds to the phase angel ending at 180° or ending at 360°.

Various conventional technologies have been used to detect whether or not a TRIAC dimmer has been included in a lighting system, and if a TRIAC dimmer is detected to be included in the lighting system, whether the TRIAC dimmer is a leading-edge TRIAC dimmer or a trailing-edge TRIAC dimmer. In one conventional technology, a rectified output voltage generated by a rectifier is compared with a threshold voltage V_(th) _(_) _(on) in order to determine a turn-on time period T_(on). If the turn-on time period T_(on) is equal to the duration of a half cycle of the AC input voltage, no TRIAC dimmer is determined to be included in the lighting system; if the turn-on time period T_(on) is smaller than the duration of a half cycle of the AC input voltage, a TRIAC dimmer is determined to be included in the lighting system. If a TRIAC dimmer is determined to be included in the lighting system, a turn-on voltage V_(on) is compared with the threshold voltage V_(th) _(_) _(on). If the turn-on voltage V_(on) is larger than the threshold voltage V_(th) _(_) _(on), the TRIAC dimmer is determined to be a leading-edge TRIAC dimmer; if the turn-on voltage V_(on) is smaller than the threshold voltage V_(th) _(_) _(on), the TRIAC dimmer is determined to be a trailing-edge TRIAC dimmer.

In another conventional technology, a rate of change of a rectified output voltage is used. The rectified output voltage is generated by a rectifier, and its rate of change is determined by quickly sampling the rectified voltage twice. Depending on the phase angles at which these two sampling actions are taken, a predetermined range for the rate of change is used. If the rate of change falls within this predetermined range, no TRIAC dimmer is determined to be included in the lighting system; if the rate of change falls outside this predetermined range, a TRIAC dimmer is determined to be included in the lighting system. If a TRIAC dimmer is determined to be included in the lighting system, whether the rate of change is positive or negative is used to determine the type of the TRIAC dimmer. If the rate of change is positive, the TRIAC dimmer is determined to be a leading-edge TRIAC dimmer; if the rate of change is negative, the TRIAC dimmer is determined to be a trailing-edge TRIAC dimmer.

If a conventional lighting system includes a TRIAC dimmer and light emitting diodes (LEDs), the light emitting diodes may flicker if the current that flows through the TRIAC dimmer falls below a holding current that is, for example, required by the TRIAC dimmer. As an example, if the current that flows through the TRIAC dimmer falls below the holding current, the TRIAC dimmer may turn on and off repeatedly, thus causing the LEDs to flicker. As another example, the various TRIAC dimmers made by different manufacturers have different holding currents ranging from 5 mA to 50 mA.

In order to solve this flickering problem, certain conventional technology uses a bleeder for the conventional lighting system. FIG. 2 is a simplified diagram of a conventional lighting system that includes a bleeder. As shown, the lighting system 200 includes a TRIAC dimmer 210, a rectifier 220, a bleeder 230, an LED driver 240, and LEDs 250. The TRIAC dimmer 210 receives an AC input voltage 214 (e.g., V_(line)) and generate a voltage 212. The voltage 212 is received by the rectifier 220 (e.g., a full wave rectifying bridge), which then generates a rectified output voltage 222 and a rectified output current 260. The rectified output current 260 is equal to the current that flows through the TRIAC dimmer 210, and is also equal to the sum of currents 232 and 242. The current 232 is received by the bleeder 230, and the current 242 is received by the LED driver 240. The magnitude of the current 232 may have a fixed magnitude or may change between two different predetermined magnitudes.

FIG. 3 is a simplified diagram showing certain conventional components of the bleeder as part of the lighting system 200 as shown in FIG. 2. The bleeder 230 includes a current detection circuit 310, a logic control circuit 320, and current sinks 330 and 340. As shown in FIG. 3, a current 350 is configured to follow through a resistor 360 in order to generate a voltage 370 (e.g., V₁). The current 350 equals the rectified output current 260 in magnitude, and the voltage 370 represents the magnitude of the current 350. The voltage 370 is divided by resistors 362 and 364 to generate a voltage 372 (e.g., V₂). The voltage 372 is received by the current detection circuit 310, which sends detected information to the logic control circuit 320. In response, the logic control circuit 320 either enables the current sink 330 with a control signal 332 or enables the current sink 340 with a control signal 342. The control signals 332 and 342 are generated by the logic control circuit 320 and are complementary to each other. If the current sink 330 is enabled, the current 232 received by the bleeder 230 is equal to a current 334; if the current sink 340 is enabled, the current 232 is equal to a current 344. The current 344 is larger than the current 334 in magnitude.

Returning to FIG. 2, the voltage 212 generated by the TRIAC dimmer 210 may have waveforms that are not symmetric between a positive half cycle and a negative half cycle of the AC input voltage 214. This lack of symmetry can cause the current that flows through the LEDs 250 to vary with time; therefore, the LEDs 250 can flicker at a fixed frequency (e.g., 50 Hz or 60 Hz). Also, according to certain conventional technology, a single TRIAC dimmer (e.g., the TRIAC dimmer 210) and a single rectifier (e.g., the rectifier 220) are used to support multiple lamp subsystems that are connected in parallel. Each lamp subsystem includes a bleeder (e.g., the bleeder 230), an LED driver (e.g., the LED driver 240), and LEDs (e.g., LEDs 250), and is associated with a rectified output current (e.g., the rectified output current 260) that provides currents to the bleeder (e.g., the bleeder 230) and the LED driver (e.g., the LED driver 240). The sum of these rectified output currents of multiple lamp subsystems is equal to the current that flows through the TRIAC dimmer (e.g., the TRIAC dimmer 210). Often, each rectified output current for each lamp subsystem is made larger than the holding current of the TRIAC dimmer (e.g., the TRIAC dimmer 210); hence the sum of these rectified output currents become much larger than the holding current of the TRIAC dimmer (e.g., the TRIAC dimmer 210), wasting of energy and thus lowering efficiency of the system.

Hence it is highly desirable to improve the techniques of dimming control.

3. BRIEF SUMMARY OF THE INVENTION

Certain embodiments of the present invention are directed to integrated circuits. More particularly, some embodiments of the invention provide a system and method for intelligent control related to TRIAC dimmers. Merely by way of example, some embodiments of the invention have been applied to driving light emitting diodes (LEDs). But it would be recognized that the invention has a much broader range of applicability.

According to one embodiment, a system controller for a lighting system includes a first controller terminal configured to receive a first signal, and a second controller terminal configured to output a second signal to a diver component. The driver component is configured to receive a first current and provide one or more drive currents to one or more light emitting diodes in response to the second signal. Additionally, the system controller is configured to process information associated with the first signal, determine a first time period for the first signal to increase from a first threshold to a second threshold, and determine a second time period for the first signal to decrease from the second threshold to the first threshold. Moreover, the system controller is further configured to, in response to the second time period minus the first time period being larger than a predetermined positive value, determine the first signal to be associate with a leading-edge TRIAC dimmer, and in response to the first time period minus the second time period being larger than the predetermined positive value, determine the first signal to be associate with a trailing-edge TRIAC dimmer. Also, the system controller is further configured to, in response to an absolute value of the first time period minus the second time period being smaller than the predetermined positive value, determine the first signal not to be associated with any TRIAC dimmer.

According to another embodiment, a system controller for a lighting system includes a first controller terminal configured to receive a first signal associated with a TRIAC dimmer, and a second controller terminal configured to output a second signal to a current sink. The current sink is configured to receive a first current in response to the second signal. Additionally, the system controller includes a third controller terminal configured to output a third signal to a driver component. The driver component is configured to receive a second current and provide one or more drive currents to one or more light emitting diodes in response to the third signal. Moreover, the system controller includes a fourth controller terminal configured to receive a fourth signal. The fourth signal is related to a third current that flows through the TRIAC dimmer. Also, the system controller is configured to process information associated with the first signal, and determine the TRIAC dimmer is turned on at a first time based at least in part on the first signal. Additionally, the system controller is configured to, after the first time, with a first delay, decrease a duty cycle of the second signal from a first predetermined value until the fourth signal indicates that the TRIAC dimmer is turned off at a second time, and in response to the fourth signal indicating that the TRIAC dimmer is turned off at the second time, set a first threshold for the fourth signal, the first threshold being related to a holding current of the TRIAC dimmer. Moreover, the system controller is further configured to process information associated with the first signal, and determine the TRIAC dimmer is turned on at a third time based at least in part on the first signal. Also, the system controller is further configured to, after the third time, with a second delay, change the second signal from a first logic level to a second logic level and keep the second signal at the second logic level until a fourth time, and at the fourth time, change the second signal to a modulation signal to regulate the fourth signal at a second threshold in order to keep the fourth signal larger than the first threshold and keep the third current larger than the holding current of the TRIAC dimmer. The second threshold is larger than the first threshold, and the modulation signal changes between the first logic level and the second logic level.

According to yet another embodiment, a method for a lighting system includes receiving a first signal, processing information associated with the first signal, determining a first time period for the first signal to increase from a first threshold to a second threshold, determining a second time period for the first signal to decrease from the second threshold to the first threshold, and processing information associated with the first time period and the second time period. Additionally, the method includes, in response to the second time period minus the first time period being larger than a predetermined positive value, determining the first signal to be associate with a leading-edge TRIAC dimmer, and in response to the first time period minus the second time period being larger than the predetermined positive value, determining the first signal to be associate with a trailing-edge TRIAC dimmer. Moreover, the method includes, in response to an absolute value of the first time period minus the second time period being smaller than the predetermined positive value, determining the first signal not to be associated with any TRIAC dimmer.

According to yet another embodiment, a method for a lighting system includes receiving a first signal associated with a TRIAC dimmer, receiving a second signal related to a first current that flows through the TRIAC dimmer, processing information associated with the first signal, and determining the TRIAC dimmer is turned on at a first time based at least in part on the first signal. Additionally, the method includes, after the first time, with a first delay, decreasing a duty cycle of a third signal from a first predetermined value until the second signal indicates that the TRIAC dimmer is turned off at a second time, and setting a first threshold for the second signal in response to the second signal indicating that the TRIAC dimmer is turned off at the second time, the first threshold being related to a holding current of the TRIAC dimmer. Moreover, the method includes determining that the TRIAC dimmer is turned on at a third time based at least in part on the first signal, and after the third time, with a second delay, changing the third signal from a first logic level to a second logic level and keep the third signal at the second logic level until a fourth time. Also, the method includes at the fourth time, changing the third signal to a modulation signal to regulate the second signal at a second threshold in order to keep the second signal larger than the first threshold and keep the first current larger than the holding current of the TRIAC dimmer. The second threshold is larger than the first threshold, and the modulation signal changes between the first logic level and the second logic level.

Depending upon embodiment, one or more benefits may be achieved. These benefits and various additional objects, features and advantages of the present invention can be fully appreciated with reference to the detailed description and accompanying drawings that follow.

4. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows certain conventional timing diagrams for a leading-edge TRIAC dimmer and a trailing-edge TRIAC dimmer.

FIG. 2 is a simplified diagram of a conventional lighting system that includes a bleeder.

FIG. 3 is a simplified diagram showing certain conventional components of the bleeder as part of the lighting system as shown in FIG. 2.

FIG. 4 is a simplified diagram of a lighting system according to an embodiment of the present invention.

FIG. 5 shows certain timing diagrams for a processing component of a system controller as part of the lighting system as shown in FIG. 4 according to an embodiment of the present invention.

FIG. 6 shows certain timing diagrams for another processing component of the system controller as part of the lighting system as shown in FIG. 4 if a TRIAC dimmer is includes in the lighting system and the TRIAC dimmer is a leading-edge TRIAC dimmer according to an embodiment of the present invention.

FIG. 7 shows certain timing diagrams for yet another processing component of the system controller as part of the lighting system as shown in FIG. 4 if a TRIAC dimmer is includes in the lighting system and the TRIAC dimmer is a leading-edge TRIAC dimmer according to an embodiment of the present invention.

FIG. 8 is a simplified diagram of a lighting system that includes multiple lamp subsystems according to an embodiment of the present invention.

FIG. 9 is a simplified diagram of a lighting system that includes multiple lamp subsystems according to another embodiment of the present invention.

5. DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the present invention are directed to integrated circuits. More particularly, some embodiments of the invention provide a system and method for intelligent control related to TRIAC dimmers. Merely by way of example, some embodiments of the invention have been applied to driving light emitting diodes (LEDs). But it would be recognized that the invention has a much broader range of applicability.

As discussed earlier, various conventional technologies have been used to detect whether or not a TRIAC dimmer has been included in a lighting system, and if a TRIAC dimmer is detected to be included in the lighting system, whether the TRIAC dimmer is a leading-edge TRIAC dimmer or a trailing-edge TRIAC dimmer. These conventional technologies have various weaknesses.

In one conventional technology, a rectified output voltage generated by a rectifier is compared with a threshold voltage V_(th) _(_) _(on) in order to determine a turn-on time period T_(on). This conventional technology, however, often cannot effectively distinguish the situation where no TRIAC dimmer is included in a lighting system from the situation where a trailing-edge TRIAC dimmer is included in a lighting system. In the situation where a trailing-edge TRIAC dimmer is included in a lighting system, the voltage generated by the trailing-edge TRIAC dimmer after the dimmer is turned off decreases slowly to the threshold voltage V_(th) _(_) _(on) due to charging and/or discharging of one or more capacitors. This slow reduction of the voltage makes it difficult to compare the turn-on time period T_(on) and the duration of a half cycle of the AC input voltage; hence the determination about whether a TRIAC dimmer has been included in a lighting system and/or whether a trailing-edge TRIAC dimmer has been included in a lighting system becomes unreliable.

In another conventional technology, a rate of change of a rectified output voltage is used. The rectified output voltage is generated by a rectifier, and its rate of change is determined by quickly sampling the rectified voltage twice. Hence this conventional technology needs real-time fast calculation of rate of change between two successively sampled rectified voltage values, and also needs storage of various predetermined ranges for the rate of change that correspond to various phase angles at which these two sampling actions are taken. Such computation and storage often impose significant demand on bit depth of an analog-to-digital converter, computational capability of the system, and storage capacity of the system.

Additionally, referring to FIG. 2, the current 232 is received by the bleeder 230. As shown in FIG. 3, the magnitude of the current 232 can change between two different predetermined magnitudes. The current 232 equals the current 334 or the current 344, and the current 344 is larger than the current 334 in magnitude. One weakness of this conventional technology as shown in FIGS. 2 and 3 is that the currents 334 and 344 each have a fixed magnitude. If the holding current of the TRIAC dimmer 210 is higher than both the currents 334 and 344 in magnitude, the LEDs 250 may flicker. If the holding current of the TRIAC dimmer 210 is lower than the current 344 but higher than the current 334 in magnitude, setting the current 232 equal to the current 334 may cause the LEDs 250 to flicker, but setting the current 232 equal to the current 344 may waster energy and thus lower efficiency of the system.

Moreover as discussed above, as shown in FIG. 2, the voltage 212 generated by the TRIAC dimmer 210 may have waveforms that are not symmetric between a positive half cycle and a negative half cycle of the AC input voltage 214. This lack of symmetry can cause the LEDs 250 to flicker at a fixed frequency (e.g., 50 Hz or 60 Hz). To resolve this issue, two turn-on time periods for the waveforms can be detected in real time. One of the two turn-on time periods corresponds to a positive half cycle, and the other of the two turn-on time periods corresponds to a negative half cycle that is neighboring to the positive half cycle. The waveform with the longer turn-on time period can, for example, be delayed in providing a current to the LEDs 250, so that the current received by the LEDs 250 is symmetric between the positive half cycle and the negative half cycle of the AC input voltage 214.

Additionally as discussed above, according to certain conventional technology, a single TRIAC dimmer (e.g., the TRIAC dimmer 210) and a single rectifier (e.g., the rectifier 220) are used to support multiple lamp subsystems that are connected in parallel. The sum of the rectified output currents of multiple lamp subsystems is equal to the current that flows through the TRIAC dimmer (e.g., the TRIAC dimmer 210), and often is much larger than the holding current of the TRIAC dimmer (e.g., the TRIAC dimmer 210). Such large magnitude for the sum of the rectified output currents of multiple lamp subsystems not only lowers efficiency of the system but also reduces the number of lamp subsystems that can be supported by the single TRIAC dimmer (e.g., the TRIAC dimmer 210) and the single rectifier (e.g., the rectifier 220).

Certain embodiments of the present invention provide an intelligent mechanism to match and control a TRIAC dimmer. According to one embodiment, the intelligent mechanism can reliably and automatically detect whether or not a TRIAC dimmer has been included in a lighting system, and if a TRIAC dimmer is detected to be included in the lighting system, whether the TRIAC dimmer is a leading-edge TRIAC dimmer or a trailing-edge TRIAC dimmer. For example, this reliable and automatic detection can help to select appropriate method of dimming control in order to improve energy efficiency of the system. According to another embodiment, the intelligent mechanism can automatically detect the holding current of the TRIAC dimmer, and use the closed-loop control to ensure the current that flows through the TRIAC dimmer is not lower than the holding current of the TRIAC dimmer.

According to another embodiment, the intelligent mechanism can provide to LEDs a current that is symmetric between the positive half cycle and the negative half cycle of an AC input voltage in order to prevent flickering of the LEDs that can be caused by an asymmetric current between the positive half cycle and the negative half cycle of the AC input voltage. According to yet another embodiment, if multiple lamp subsystems are connected in parallel, the intelligent mechanism can optimize each rectified output current for each lamp subsystem so that the sum of these rectified output currents is larger than but not too much larger than the holding current of the TRIAC dimmer in order to avoid flickering of LEDs that is caused by insufficient current flowing through the TRIAC dimmer. For example, such optimization of each rectified output current can help improve energy efficiency of the system. In another example, such optimization of each rectified output current can increase the number of lamp subsystems that can be supported by the system.

FIG. 4 is a simplified diagram of a lighting system according to an embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. The lighting system 400 includes a TRIAC dimmer 410, a rectifier 420, a current sink 430, an LED driver 440, one or more LEDs 450, resistors 470, 472, 474, 476, and 478, and a system controller 480.

Although the above has been shown using a selected group of components for the lighting system 400, there can be many alternatives, modifications, and variations. In one embodiment, the TRIAC dimmer 410 is removed from the lighting system 400 so that the lighting system 400 does not include the TRIAC dimmer 410. In another embodiment, the TRIAC dimmer 410 and the rectifier 420 are used to support multiple lamp subsystems that are connected in parallel.

For example, each lamp subsystem includes a system controller (e.g., the system controller 480), and resistors (e.g., the resistors 470, 472, 474, 476, and 478), a current sink (e.g., the current sink 430), an LED driver (e.g., the LED driver 440), and one or more LEDs (e.g., the one or more LEDs 450). In another example, each lamp subsystem includes a rectifier (e.g., the rectifier 420), a system controller (e.g., the system controller 480), and resistors (e.g., the resistors 470, 472, 474, 476, and 478), a current sink (e.g., the current sink 430), an LED driver (e.g., the LED driver 440), and one or more LEDs (e.g., the one or more LEDs 450).

As shown in FIG. 4, the TRIAC dimmer 410 receives an AC input voltage 414 (e.g., V_(line)) and generates a voltage 412. For example, the voltage 412 is received by the rectifier 420 (e.g., a full wave rectifying bridge), which generates a rectified output voltage 422 and a rectified output current 460. In another example, the rectified output voltage 422 is received by a voltage divider including the resistors 470 and 472, and the voltage divider outputs a voltage 424.

In one embodiment, a current 464 flows through the resistor 478, which generates a voltage 466. For example, the current 464 is equal to the rectified output current 460 in magnitude. In another example, the voltage 466 is received by a voltage divider including the resistors 474 and 476, and the voltage divider outputs a voltage 426. In yet another example, the voltage 426 represents the rectified output current 460, which is equal to the current that flows through the TRIAC dimmer 410.

In another embodiment, the system controller 480 includes terminals 482, 484, 486, and 488, and processing components 492, 494, and 496. For example, the terminal 482 (e.g., the terminal “V_DET”) receives the voltage 424. In another example, the terminal 484 (e.g., the terminal “I_DET”) receives the voltage 426. In yet another example, the terminal 486 (e.g., the terminal “BL”) outputs a control signal 434 (e.g., a pulse-width-modulation signal or an analog voltage signal) to the current sink 430. In yet another example, the terminal 488 (e.g., the terminal “DIM”) outputs a control signal 436 (e.g., a pulse-width-modulation signal or an analog voltage signal) to the LED driver 440.

In yet another embodiment, the current sink 430, in response to the received signal 434, generates a current 432. For example, the signal 434 is an analog voltage signal that controls the magnitude of the current 432. In another example, the received signal 434 is a logic signal, which changes between a logic high level and a logic low level. According to one embodiment, if the received signal 434 is at the logic high level, the current sink 430 is turned on and the current 432 is equal to a predetermined current level that is larger than zero, and if the received signal 434 is at the logic low level, the current sink 430 is turned off and the current 432 is equal to zero. According to another embodiment, the ratio between the time period when the received signal 434 is at the logic high level and the time period when the received signal 434 is at the logic low level is used by the current sink 430 to determine the magnitude of the current 432. For example, if the ratio becomes smaller, the current 432 also becomes smaller in magnitude.

In yet another embodiment, the LED driver 440 is configured to receive the signal 436 and a current 442, and provide one or more drive currents to drive the one or more LEDs 450 in response to the signal 436. For example, the control signal 436 is a logic signal. In another example, if the control signal 436 is at the logic high level, the LED driver in response receives the current 442 and provides one or more drive currents to drive the one or more LEDs 450. In yet another example, if the control signal 436 is at the logic low level, in response, the current 442 is equal to zero and the one or more drive currents are also equal to zero. In yet another example, the control signal 436 is an analog signal, and the LED driver in response receives the current 442 and provides one or more drive currents to drive the one or more LEDs 450, where the one or more drive currents are proportional to the magnitude of the control signal 436.

In yet another embodiment, the rectified output current 460 is equal to the current that flows through the TRIAC dimmer 410, and is divided into a current 462 received by the resistor 470, the current 432 generated and received by the current sink 430, and the current 442 received by the LED driver 440. For example, the rectified output current 460 is equal to the sum of the current 462, the current 432, and the current 442. In another example, the rectified output current 460 is equal to the current 464 that is received by the resistor 478 in magnitude.

In yet another embodiment, the processing component 492 is configured to detect whether or not the TRIAC dimmer 410 is included in the lighting system 400, and if the TRIAC dimmer 410 is detected to be included in the lighting system 400, whether the TRIAC dimmer 410 is a leading-edge TRIAC dimmer or a trailing-edge TRIAC dimmer. For example, the processing component 494 is configured to detect the holding current of the TRIAC dimmer 410, and use the closed-loop control to control the current 432. In another example, the processing component 496 is configured to process the voltage 424 that has waveforms not symmetric between a positive half cycle and a negative half cycle of the AC input voltage 414, so that the system controller 480 can provide to the one or more LEDs 450 a current that is symmetric between the positive half cycle and the negative half cycle of the AC input voltage 414. In yet another example, the processing component 492 is configured to, if the lighting system 400 includes the multiple lamp subsystems, control the current 432 for the lamp subsystem to which the system controller 480 belongs.

In yet another embodiment, the following processes (a), (b), and (c) are performed sequentially:

-   -   (a) The system controller 480 uses the processing component 492         to detect whether or not the TRIAC dimmer 410 is included in the         lighting system 400, and if the TRIAC dimmer 410 is detected to         be included in the lighting system 400, whether the TRIAC dimmer         410 is a leading-edge TRIAC dimmer or a trailing-edge TRIAC         dimmer;     -   (b) After the process (a) as described above, if the process (a)         determines the TRIAC dimmer 410 is included in the lighting         system 400, the system controller 480 uses the processing         component 494 to detect the holding current of the TRIAC dimmer         410; and     -   (c) After the processes (a) and (b) as described above, the         process (c) is performed. During the process (c), the system         controller 480 uses the processing component 494 to rely on the         closed-loop control to control the current 432. Additionally,         during the process (c), the system controller 480 uses the         processing component 496 to process the voltage 424 that has         waveforms not symmetric between a positive half cycle and a         negative half cycle of the AC input voltage 414, so that the         system controller 480 can provide to the one or more LEDs 450 a         current that is symmetric between the positive half cycle and         the negative half cycle of the AC input voltage 414.

As discussed above and further emphasized here, FIG. 4 is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. In one embodiment, the TRIAC dimmer 410 is removed from the lighting system 400, so that the lighting system 400 does not include the TRIAC dimmer 410 and the rectifier 420 directly receives the AC input voltage 414 and generates the rectified output voltage 422 and the rectified output current 460. In another embodiment, some (e.g., one or two) of the processing components 492, 494, and 496 are removed from the system controller 480.

As shown in FIG. 4, when the lighting system 400 is just turned on, the duty cycle of the signal 436 is equal to zero and hence the LED driver 440 does not operate according to certain embodiments. In one embodiment, immediately after the lighting system 400 is turned on, the system controller 480 uses the processing component 492 to first detect whether or not the TRIAC dimmer 410 is included in the lighting system 400, and if the TRIAC dimmer 410 is detected to be included in the lighting system 400, whether the TRIAC dimmer 410 is a leading-edge TRIAC dimmer or a trailing-edge TRIAC dimmer. In another embodiment, the processing component 492 uses the received voltage 424 to detect a rising time period (e.g., T_rise) during which the voltage 424 increases from a lower threshold voltage (e.g., Vth_off) to a higher threshold voltage (e.g., Vth_on) and to detect a falling time period (e.g., T_fall) during which the voltage 424 decreases from the higher threshold voltage (e.g., Vth_on) to the lower threshold voltage (e.g., Vth_off). For example, the processing component 492 compares the detected rising time (e.g., T_rise) and the detected falling time (e.g., T_fall) to determine whether or not the TRIAC dimmer 410 is included in the lighting system 400, and if the TRIAC dimmer 410 is determined to be included in the lighting system 400, whether the TRIAC dimmer 410 is a leading-edge TRIAC dimmer or a trailing-edge TRIAC dimmer.

FIG. 5 shows certain timing diagrams for the processing component 492 of the system controller 480 as part of the lighting system 400 as shown in FIG. 4 according to an embodiment of the present invention. These diagrams are merely examples, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications.

For example, the waveform 510 represents the voltage 424 as a function of time during a half cycle of the AC input voltage 414 (e.g., V_(line)) if the lighting system 400 does not include the TRIAC dimmer 410 so that the rectifier 420 directly receives the AC input voltage 414 and generates the rectified output voltage 422 and the rectified output current 460. In another example, the waveform 520 represents the voltage 424 as a function of time during a half cycle of the AC input voltage 414 (e.g., V_(line)) if the lighting system 400 includes the TRIAC dimmer 410 and the TRIAC dimmer 410 is a leading-edge TRIAC dimmer. In yet another example, the waveform 530 represents the voltage 424 as a function of time during a half cycle of the AC input voltage 414 (e.g., V_(line)) if the lighting system 400 includes the TRIAC dimmer 410 and the TRIAC dimmer 410 is a trailing-edge TRIAC dimmer.

According to one embodiment, if the detected rising time (e.g., T_rise) is equal to or approximately equal to the detected falling time (e.g., T_fall), the processing component 492 determines that the TRIAC dimmer 410 is not included in the lighting system 400. According to another embodiment, if the detected rising time (e.g., T_rise) is smaller than the detected falling time (e.g., T_fall), the processing component 492 determines that the TRIAC dimmer 410 is included in the lighting system 400 and the TRIAC dimmer 410 is a leading-edge TRIAC dimmer. For example, for the leading-edge TRIAC dimmer, the voltage 424 increases rapidly so that the detected rising time (e.g., T_rise) is approximately equal to zero. In another example, comparing the detected rising time (e.g., T_rise) and the detected falling time (e.g., T_fall) can reliably detect whether or not the TRIAC dimmer 410 in the lighting system 400 is a leading-edge TRIAC dimmer. According to yet another embodiment, if the detected rising time (e.g., T_rise) is larger than the detected falling time (e.g., T_fall), the processing component 492 determines that the TRIAC dimmer 410 is included in the lighting system 400 and the TRIAC dimmer 410 is a trailing-edge TRIAC dimmer. For example, for the trailing-edge TRIAC dimmer, the voltage 424 decreases slowly due to charging and/or discharging of one or more capacitors so that the detected falling time (e.g., T_fall) is not approximately equal to zero. In another example, comparing the detected rising time (e.g., T_rise) and the detected falling time (e.g., T_fall) can reliably distinguish the situation where the TRIAC dimmer 410 is not included in the lighting system 400 from the situation where the TRIAC dimmer 410 in the lighting system 400 is a trailing-edge TRIAC dimmer.

According to certain embodiments, where AT is a predetermined threshold,

-   -   (a) if |T_rise−T_fall|≦ΔT, the processing component 492         determines that the TRIAC dimmer 410 is not included in the         lighting system 400;     -   (b) if T_fall−T_rise>ΔT, the processing component 492 determines         that the TRIAC dimmer 410 is included in the lighting system 400         and the TRIAC dimmer 410 is a leading-edge TRIAC dimmer; and     -   (c) if T_rise−T_fall>ΔT, the processing component 492 determines         that the TRIAC dimmer 410 is included in the lighting system 400         and the TRIAC dimmer 410 is a trailing-edge TRIAC dimmer.

As shown in FIG. 4, after the processing component 492 has detected that the TRIAC dimmer 410 is included in the lighting system 400, and also determined whether the TRIAC dimmer 410 is a leading-edge TRIAC dimmer or a trailing-edge TRIAC dimmer, the processing component 494 is configured to detect the holding current of the TRIAC dimmer 410, and use the closed-loop control to control the current 432 according to certain embodiments.

FIG. 6 shows certain timing diagrams for the processing component 494 of the system controller 480 as part of the lighting system 400 as shown in FIG. 4 if the TRIAC dimmer 410 is includes in the lighting system 400 and the TRIAC dimmer 410 is a leading-edge TRIAC dimmer 410 according to an embodiment of the present invention. These diagrams are merely examples, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. According to some embodiments, the waveform 610 represents the voltage 424 as a function of time, the waveform 620 represents the signal 434 as a function of time, the waveform 630 represents the signal 436 as a function of time, and the waveform 640 represents the voltage 426 as a function of time. According to certain embodiments, the processing component 494 is configured to detect the holding current of the TRIAC dimmer 410 before time t_(s), and use the closed-loop control to control the current 432 after time t_(s).

In one embodiment, the processing component 494 receives the voltage 424, and based on the received voltage 424, determines that the TRIAC dimmer 410 is turned on at time t₁, as shown by the waveform 610. In response, after time t₁, the system controller 480, including the processing component 494, generates the signal 434 so that the signal 434 is at the maximum duty cycle immediately after time t₁, but the duty cycle of the signal 434 then decreases with time from the maximum duty cycle, according to some embodiments. For example, if the signal 434 is at the maximum duty cycle, the current 432 reaches a maximum magnitude. In another example, if the current 432 reaches a maximum magnitude, the current 460 also reaches a maximum magnitude and the voltage 426 reaches a corresponding maximum magnitude at time t₂, as shown by the waveform 640. In yet another example, the maximum magnitude of the current 460 is high than the holding current of the TRIAC dimmer 410, so that the TRIAC dimmer 410 remains to be turned on at time t₂.

In yet another embodiment, if the duty cycle of the signal 434 decreases with time from the maximum duty cycle as shown by the waveform 610, the voltage 426, which represents the current 460, also decreases with time from the maximum magnitude as shown by the waveform 640. For example, if the current 460, which is equal to the current flowing through the TRIAC dimmer 410, becomes smaller than the holding current of the TRIAC dimmer 410, the TRIAC dimmer 410 is turned off. In yet another example, in response to the TRIAC dimmer 410 being turned off, the decrease of the voltage 424 becomes steeper at time t₃ as shown by the waveform 610 and the decrease of the voltage 426 also becomes steeper at time t₃ as shown by the waveform 640. In yet another example, the processing component 494 is configured to detect an abrupt change of slope at which the voltage 426 decreases, and set a threshold magnitude V_(A) for the voltage 426 based at least in part on the detected abrupt change of slope.

In yet another embodiment, the threshold magnitude V_(A) of the voltage 426 at time t₃ corresponds to the holding current of the TRIAC dimmer 410. For example, V_(A) represents the holding current as detected by the process. In yet another embodiment, the system controller 480 sets a threshold magnitude V_(B) for the voltage 426. For example, V_(B) is larger than V_(A). In another example, V_(B)=V_(A)+ΔV₁, where ΔV₁ is a predetermined threshold and is larger than zero. In yet another example, V_(B)=k×V_(A), where k is a constant that is larger than or equal to 1.05 but smaller than or equal to 1.3. In yet another example, if the voltage 426 is approximately equal to V_(B), the current flowing through the TRIAC dimmer 410 is larger than the holding current of the TRIAC dimmer 410, so long as the voltage 426 remains larger than V_(A). In yet another example, the system controller 480 stores the threshold magnitude V_(B).

As shown in FIG. 6, after time t_(s), the processing component 494 is configured to use the threshold magnitude V_(B) to perform the closed-loop control to control the voltage 426 by controlling the current 432 according to some embodiments. For example, time t_(s) is the beginning of the next half cycle of the AC input voltage 414. In another example, the voltage 426 represents the current that flows through the TRIAC dimmer 410, so the system controller 480 controls the current flowing through the TRIAC dimmer 410 by controlling the current 432 and the voltage 426.

In one embodiment, the processing component 494 receives the voltage 424, and based on the received voltage 424, determines that the TRIAC dimmer 410 is turned on at time t₄, as shown by the waveform 610. In response, the signal 436 generated by the system controller 480 becomes a modulation signal (e.g., a pulse-width-modulation signal) at time t₄, changing between a logic high level and a logic low level according to another embodiment, as shown by the waveform 630. For example, the signal 436 remains at the logic low level from time t₁ to time t₄. In another example, the signal 436 is a modulation signal (e.g., a pulse-width-modulation signal) from time t₄ to time t₇. In yet another example, the pulse-width-modulation signal 436 has a pulse width that corresponds to the dimming control as reflected by the time duration from time t₁ to time t_(s).

In yet another embodiment, the signal 434 generated by the system controller 480 remains at the logic high level from time t₃ to time t₅, and time t₅ follows time t₄. For example, at time t₅, the signal 434 changes from the logic high level to the logic low level. In another example, from time t₄ to time t₅, the current 432 increases with time and reaches a maximum magnitude at time t₅. In yet another example, at time t₅, the current 460 also reaches a maximum magnitude and the voltage 426 reaches a corresponding maximum magnitude at time t₅, as shown by the waveform 640. In yet another example, the maximum magnitude of the current 460 is high than the holding current of the TRIAC dimmer 410, so that the TRIAC dimmer 410 remains to be turned on at time t₅.

In yet another embodiment, from time t₅ and time t₆, the signal 434 remains at the logic low level. For example, from time t₅ and time t₆, the voltage 426 becomes smaller than the corresponding maximum magnitude that the voltage 426 reaches at time t₅. In another example, at time t₆, the voltage 426 becomes smaller than V_(B)+ΔV₂, even though the voltage 426 is still larger than V_(B), where V_(B) represents the threshold magnitude that is stored by the system controller 480, and ΔV₂ represents a predetermined threshold that is larger than zero. In yet another example, at time t₆, in response to the voltage 426 becoming becomes smaller than V_(B)+ΔV₂, even though still larger than the threshold magnitude V_(B), the signal 434 generated by the system controller 480 becomes a modulation signal at time t₆, changing between a logic high level and a logic low level, as shown by the waveform 620.

According to one embodiment, the signal 434 is a modulation signal from time t₆ to time t₇. For example, from time t₆ to time t₇, the signal 434 as a modulation signal regulates the voltage 426 at the threshold magnitude V_(B), and the voltage 426 becomes approximately equal to the threshold magnitude V_(B) by a closed-loop regulation, so that the voltage 426 remains larger than the magnitude V_(A) of the voltage 426 from time t₆ to time t₇, where the magnitude V_(A) of the voltage 426 corresponds to the holding current of the TRIAC dimmer 410.

In another example, from time t₆ to time t₇, the current flowing through the TRIAC dimmer 410 remains larger than the holding current of the TRIAC dimmer 410, so that the TRIAC dimmer 410 is not turned off by the insufficient current flowing through the TRIAC dimmer 410.

According to another embodiment, time t₇ is the end of the half cycle of the AC input voltage 414 that starts at time t_(s), and time t₇ is also the beginning of another half cycle of the AC input voltage 414. For example, as shown by the waveform 610, the voltage 424 becomes zero at time t₇ and remains to be zero until the TRIAC dimmer 410 is turned on. In another example, as shown by the waveform 620, the signal 434 is at the logic high level at time t₇, and remains at the logic high level until sometime after the TRIAC dimmer 410 is turned on. In yet another example, as shown by the waveform 630, the signal 436 is at the logic low level at time t₇, and remains at the logic low level until the TRIAC dimmer 410 is turned on. In yet another example, as shown by the waveform 640, the voltage 426 decreases to zero soon after time t₇, and remains to be zero until the TRIAC dimmer 410 is turned on.

As discussed above and further emphasized here, FIG. 6 is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. For example, the waveforms 610, 620, 630 and 640 are changed if the TRIAC dimmer 410 is includes in the lighting system 400 and the TRIAC dimmer 410 is a trailing-edge TRIAC dimmer, instead of a leading-edge TRIAC dimmer 410. In another example, the waveforms 610, 620, 630 and 640 are changed if the TRIAC dimmer 410 is not included in the lighting system 400. In yet another example, FIG. 6 is used to describe certain operations of FIG. 8. In yet another example, FIG. 6 is used to describe certain operations of FIG. 9.

As shown in FIG. 4, the processing component 496 is configured to process the voltage 424 that has waveforms not symmetric between a positive half cycle and a negative half cycle of the AC input voltage 414, so that the system controller 480 can provide to the one or more LEDs 450 a current that is symmetric between the positive half cycle and the negative half cycle of the AC input voltage 414 according to some embodiments.

FIG. 7 shows certain timing diagrams for the processing component 496 of the system controller 480 as part of the lighting system 400 as shown in FIG. 4 if the TRIAC dimmer 410 is includes in the lighting system 400 and the TRIAC dimmer 410 is a leading-edge TRIAC dimmer 410 according to an embodiment of the present invention. These diagrams are merely examples, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. According to some embodiments, the waveform 710 represents the voltage 424 as a function of time, the waveform 720 represents the signal 436 as a function of time, and the waveform 730 represents the current that flows through the one or more LEDs 450 as a function of time. According to certain embodiments, the processing component 496 is configured to work with the processing component 494, wherein the processing component 494 uses the closed-loop control to control the current 432 and the processing component 496 processes the voltage 424 that has waveforms not symmetric between a positive half cycle and a negative half cycle of the AC input voltage 414.

In one embodiment, the processing component 494 receives the voltage 424, and based on the received voltage 424, determines that the TRIAC dimmer 410 is turned on at time t₄, as shown by the waveform 710. In response, the signal 436 generated by the system controller 480 becomes a modulation signal (e.g., a pulse-width-modulation signal) at time t₄, changing between a logic high level and a logic low level according to another embodiment, as shown by the waveform 720. For example, the signal 436 is at the logic low level before time t₄. In another example, the signal 436 is a modulation signal (e.g., a pulse-width-modulation signal) from time t₄ to time t₇. In yet another embodiment, time t₇ is the end of the half cycle of the AC input voltage 414, during which the voltage 426 has a pulse width of T_(a) from time t₄ to time t₇. For example, time t₇ is also the beginning of another half cycle of the AC input voltage 414, during which the voltage 426 has a pulse width of T_(b) from time t₈ to time t₁₀. In another example, the pulse width of T_(b) is larger than the pulse width of T_(a).

According to one embodiment, the processing component 494 detects the pulse width of T_(a) and the pulse width of T_(b), which correspond to two successive half cycles of the AC input voltage 414, and the processing component 494 also determines that the pulse width of T_(b) is larger than the pulse width of T_(a). For example, the processing component 494 detects the pulse width T_(b) during the half cycle of the AC input voltage 414 that ends at time t_(s), and detects the pulse width T_(a) during the half cycle of the AC input voltage 414 that starts at time t_(s).

According to another embodiment, the processing component 494 receives the voltage 424, and determines that the TRIAC dimmer 410 is turned on at time t₈ with the pulse width of T_(b) for the voltage 424 as shown by the waveform 710. In response, the system controller 480, for example, keeps the signal 436 at the logic level from time t₈ to time t₉; then, at time t₉, the signal 436 becomes a modulation signal (e.g., a pulse-width-modulation signal) that changes between a logic high level and a logic low level as shown by the waveform 720. In another example, the signal 436 is a modulation signal (e.g., a pulse-width-modulation signal) from time t₉ to time t₁₀. In yet another example, the time duration from time t₉ to time t₁₀ is equal to the pulse width of T_(a), the same as the time duration from time t₄ to time t₇.

According to yet another embodiment, time t₁₀ is the end of the half cycle of the AC input voltage 414, during which the voltage 426 has a pulse width of T_(b) from time t₈ to time t₁₀. For example, time t₁₀ is also the beginning of another half cycle of the AC input voltage 414, during which the voltage 426 has a pulse width of T_(a) from time t₁₁ to time t₁₂. In response, for example, the signal 436 generated by the system controller 480, at time t₁₁, becomes a modulation signal (e.g., a pulse-width-modulation signal) that changes between a logic high level and a logic low level as shown by the waveform 720. In another example, the signal 436 is a modulation signal (e.g., a pulse-width-modulation signal) from time t₁₁ to time t₁₂. In yet another example, the time duration from time t₁₁ to time t₁₂ is equal to the pulse width of T_(a), the same as the time duration from time t₉ to time t₁₀.

According to yet another embodiment, the processing component 494 receives the voltage 424, and determines that the TRIAC dimmer 410 is turned on at time t₁₃ with the pulse width of T_(b) for the voltage 424 as shown by the waveform 710. In response, the system controller 480, for example, keeps the signal 436 at the logic level from time t₁₃ to time t₁₄; then, at time t₁₄, the signal 436 becomes a modulation signal (e.g., a pulse-width-modulation signal) that changes between a logic high level and a logic low level as shown by the waveform 720. In another example, the signal 436 is a modulation signal (e.g., a pulse-width-modulation signal) from time t₁₄ to time t₁₅. In yet another example, the time duration from time t₁₄ to time t₁₅ is equal to the pulse width of T_(a), the same as the time duration from time t₉ to time t₁₀. According to yet another embodiment, time t₁₅ is the end of the half cycle of the AC input voltage 414, during which the voltage 426 has a pulse width of T_(b) from time t₁₃ to time t₁₅. For example, time t₁₅ is also the beginning of another half cycle of the AC input voltage 414, during which the voltage 426 has a pulse width of T_(a).

As shown in FIG. 7, even though the pulse width of the voltage 424 is equal to T_(a) in the half cycle I of the AC input voltage 414, is equal to T_(b) in the half cycle II of the AC input voltage 414, is equal to T_(a) in the half cycle III of the AC input voltage 414, and is equal to T_(b) in the half cycle IV of the AC input voltage 414, the signal 436 is a modulation signal (e.g., a pulse-width-modulation signal) for a time duration equal to the pulse width of T_(a) in each of the half cycle I of the AC input voltage 414, the half cycle II of the AC input voltage 414, the half cycle III of the AC input voltage 414, and the half cycle IV of the AC input voltage 414, according to certain embodiments. For example, the pulse width of T_(b) is larger than the pulse width of T_(a). In another example, as shown by the waveform 710, the pulse width of the voltage 424 changes from one half cycle of the AC input voltage 414 to another half cycle I of the AC input voltage 414, but the current that flows through the one or more LEDs 450 remains periodic as shown by the waveform 730. In yet another example, the waveform for the current that flows through the one or more LEDs 450 changes in the same way during the time period A (e.g., from time t₄ to time t₉), the time period B (e.g., from time t₉ to time t₁₁), and the time period C (e.g., from time t₁₁ to time t₁₃). In yet another example, the waveform for the current that flows through the one or more LEDs 450 is symmetric between a positive half cycle and a negative half cycle of the AC input voltage 414 (e.g., between the half cycle II and the half cycle III as shown in FIG. 7).

FIG. 8 is a simplified diagram of a lighting system that includes multiple lamp subsystems according to an embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. The lighting system 800 includes a TRIAC dimmer 410, a rectifier 420, and multiple lamp subsystems 810 ₁, 810 ₂, . . . 810 _(i), . . . and 810 _(N), wherein N is an integer that is larger than 1, and i is an integer that is larger than or equal to 1 and is smaller than or equal to N.

In one embodiment, each of the multiple lamp subsystems includes a current sink (e.g., a current sink 430), an LED driver (e.g., an LED driver 440), one or more LEDs (e.g., one or more LEDs 450), resistors (e.g., resistors 470, 472, 474, 476, and 478), and a system controller (e.g., a system controller 480). For example, the system controller (e.g., the system controller 480) of each of the multiple lamp subsystems includes terminals (e.g., terminals 482, 484, 486, and 488), and processing components (e.g., processing components 492, 494, and 496). In another embodiment, the lamp subsystem 810 _(i) includes a current sink 430 _(i), an LED driver 440 _(i), one or more LEDs 450 _(i), resistors 470 _(i), 472 _(i), 474 _(i), 476 _(i), and 478 _(i), and a system controller 480 _(i).

As shown in FIG. 8, the TRIAC dimmer 410 receives an AC input voltage 414 (e.g., V_(line)) and generates a voltage 412. For example, the voltage 412 is received by the rectifier 420 (e.g., a full wave rectifying bridge), which generates a rectified output voltage 422 and a rectified output current 460. In another example, the rectified output voltage 422 is received by a voltage divider including the resistors 470 _(i) and 472 _(i), and the voltage divider outputs a voltage 424 _(i).

For example, the system controller 480 _(i) includes terminals 482 _(i), 484 _(i), 486 _(i), and 488 _(i), and processing components 492 _(i), 494 _(i), and 496 _(i). In another example, the terminal 484 _(i) (e.g., the terminal “I_DET”) receives a voltage 426 _(i). In yet another example, the terminal 486 _(i) (e.g., the terminal “BL”) outputs a control signal 434 _(i) (e.g., a pulse-width-modulation signal or an analog voltage signal) to the current sink 430 _(i) to control a current 432 _(i). In yet another example, the terminal 488 _(i) (e.g., the terminal “DIM”) outputs a control signal 436 _(i) (e.g., a pulse-width-modulation signal or an analog voltage signal) to the LED driver 440 _(i). In yet another example, the current 432 _(i) is smaller than or equal to a current 820 _(i) that flows into the lamp subsystem 810 _(i).

In yet another embodiment, the rectified output current 460 is equal to the current flowing through the TRIAC dimmer 410, and is also equal to the sum of a current 820 ₁, a current 820 ₂, . . . , a current 820 _(i), . . . and a current 820 _(N). For example, the current 820 ₁, the current 820 ₂, . . . , the current 820 _(i), . . . and the current 820 _(N) are currents that flow into the lamp subsystems 810 ₁, 810 ₂, . . . 810 _(i), . . . and 810 _(N), respectively. In another example, the current 820 ₁, the current 820 ₂, . . . , the current 820 _(i), . . . and the current 820 _(N) each are a component of the rectified output current 460, and each represent a component of the current flowing through the TRIAC dimmer 410. In yet another example, the voltage 426 _(i) represents the current 820 _(i), and also represents a component of the current flowing through the TRIAC dimmer 410.

In yet another embodiment, the current 820 _(i) is divided into a current 462 _(i) received by the resistor 470 _(i), the current 432 _(i) generated and received by the current sink 430 _(i), and a current 442 _(i) received by the LED driver 440 _(i). For example, the current 820 _(i) is equal to the sum of the current 462 _(i), the current 432 _(i), and the current 442 _(i).

According to one embodiment, after the processing component 492 _(i) has detected that the TRIAC dimmer 410 is included in the lighting system 800, and after the processing component 492 _(i) has also determined whether the TRIAC dimmer 410 is a leading-edge TRIAC dimmer or a trailing-edge TRIAC dimmer, the processing component 494 _(i) of the lamp subsystem 810 _(i) uses the closed-loop control to control the current 432 _(i). For example, the multiple lamp subsystems 810 ₁, 810 ₂, . . . 810 _(i), . . . and 810 _(N) together satisfy the following equation:

$\begin{matrix} {I_{holding} < {\sum\limits_{i = 1}^{N}\; I_{i}} < {I_{holding} \times N}} & \left( {{Equation}\mspace{14mu} 1} \right) \end{matrix}$ wherein I_(holding) represents the magnitude of the holding current of the TRIAC dimmer 410, and I_(i) represents the magnitude of the current 820 _(i). N is an integer that is larger than 1, and i is an integer that is larger than or equal to 1 and is smaller than or equal to N.

As discussed above and further emphasized here, FIG. 6 is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. For example, FIG. 6 is used to describe certain operations of FIG. 8.

According to some embodiments, the waveform 610 represents the voltage 424 _(i) as a function of time, the waveform 620 represents the signal 434 _(i) as a function of time, the waveform 630 represents the signal 436 _(i) as a function of time, and the waveform 640 represents the voltage 426 _(i) as a function of time. According to certain embodiments, all of the processing components 494 _(i) are configured to detect the holding current of the TRIAC dimmer 410 before time t_(s), and each use the closed-loop control to control the current 432 _(i) after time t_(s).

In one embodiment, the processing component 494 _(i) receives the voltage 424 _(i), and based on the received voltage 424 _(i), determines that the TRIAC dimmer 410 is turned on at time t₁, as shown by the waveform 610. In response, after time t₁, the system controller 480 _(i), including the processing component 494 _(i), generates the signal 434 _(i) so that the signal 434 _(i) is at the maximum duty cycle immediately after time t₁, but the duty cycle of the signal 434 _(i) then decreases with time from the maximum duty cycle, according to some embodiments. For example, if the signal 434 _(i) is at the maximum duty cycle, the current 432 _(i) reaches a maximum magnitude.

In another example, if all of the currents 432 _(i), where i is an integer that is larger than or equal to 1 and is smaller than or equal to N, each reach a maximum magnitude, all of the voltages 426 _(i) each reach a corresponding maximum magnitude at time t₂ as shown by the waveform 640, and the current 460 also reaches a maximum magnitude. In yet another example, the maximum magnitude of the current 460 is high than the holding current of the TRIAC dimmer 410, so that the TRIAC dimmer 410 remains to be turned on at time t₂.

In yet another embodiment, if the duty cycle of the signal 434 _(i) decreases with time from the maximum duty cycle as shown by the waveform 610, the voltage 426 _(i), which represents the current 820 _(i), also decreases with time from the maximum magnitude as shown by the waveform 640. For example, if all of the currents 820 _(i), where i is an integer that is larger than or equal to 1 and is smaller than or equal to N, each decrease with time from the maximum magnitude, the current 460 also decreases with time from its maximum magnitude. In another example, the current 460, which is equal to the current flowing through the TRIAC dimmer 410, becomes smaller than the holding current of the TRIAC dimmer 410, the TRIAC dimmer 410 is turned off.

In yet another example, in response to the TRIAC dimmer 410 being turned off, the decrease of the voltage 424 _(i) becomes steeper at time t₃ as shown by the waveform 610 and the decrease of the voltage 426 _(i) also becomes steeper at time t₃ as shown by the waveform 640.

In yet another embodiment, the magnitude V_(A) of the voltage 426 _(i) at time t₃ corresponds to one component of multiple components of the holding current of the TRIAC dimmer 410. For example, if all of the voltages 426 _(i) each are equal to their corresponding magnitudes V_(A), the current 460 is equal to the holding current of the TRIAC dimmer 410.

In yet another embodiment, the system controller 480 _(i) sets a threshold magnitude V_(B) for the voltage 426 _(i). For example, V_(B) is larger than V_(A). In another example, V_(B)=V_(A)+ΔV₁, where ΔV₁ is a predetermined threshold and is larger than zero. In yet another example, V=k×V_(A), where k is a constant that is larger than or equal to 1.05 but smaller than or equal to 1.3. In yet another example, if all of the voltages 426 _(i) each are approximately equal to their corresponding V_(B), the current flowing through the TRIAC dimmer 410 is larger than the holding current of the TRIAC dimmer 410, so long as the voltage 426 _(i) remains larger than V_(A). In yet another example, the system controller 480 _(i) stores the corresponding threshold magnitude V_(B).

As shown in FIG. 6, after time t_(s), the processing component 494 _(i) is configured to use the threshold magnitude V_(B) to perform the closed-loop control to control the voltage 426 _(i) by controlling the current 432 _(i) according to some embodiments. For example, time t_(s) is the beginning of the next half cycle of the AC input voltage 414. In another example, the voltage 426 _(i) represents the current 820 _(i), and sum of all of the currents 820 _(i) is equal to the current that flows through the TRIAC dimmer 410, so all of the system controllers 480 _(i) together can control the current flowing through the TRIAC dimmer 410 by each controlling the current 432 _(i) and the voltage 426 _(i).

In one embodiment, the processing component 494 _(i) receives the voltage 424 _(i), and based on the received voltage 424 _(i), determines that the TRIAC dimmer 410 is turned on at time t₄, as shown by the waveform 610. In response, the signal 436 _(i) generated by the system controller 480 _(i) becomes a modulation signal (e.g., a pulse-width-modulation signal) at time t₄, changing between a logic high level and a logic low level according to another embodiment, as shown by the waveform 630. For example, the signal 436 _(i) remains at the logic low level from time t₁ to time t₄. In another example, the signal 436 _(i) is a modulation signal (e.g., a pulse-width-modulation signal) from time t₄ to time t₇. In yet another example, the pulse-width-modulation signal 436 _(i) has a pulse width that corresponds to the dimming control as reflected by the time duration from time t₁ to time t_(s).

In yet another embodiment, the signal 434 _(i) generated by the system controller 480 _(i) remains at the logic high level from time t₃ to time t₅, and time t₅ follows time t₄. For example, at time t₅, the signal 434 _(i) changes from the logic high level to the logic low level. In another example, from time t₄ to time t₅, the current 432 _(i) increases with time and reaches a maximum magnitude at time t₅, so the voltage 426 _(i) reaches a corresponding maximum magnitude at time t₅, as shown by the waveform 640. In yet another example, at time t₅, all of the currents 820 _(i) each reach their corresponding maximum magnitudes, so the current 460 also reaches a maximum magnitude. In yet another example, the maximum magnitude of the current 460 is high than the holding current of the TRIAC dimmer 410, so that the TRIAC dimmer 410 remains to be turned on at time t₅.

In yet another embodiment, from time t₅ and time t₆, the signal 434 _(i) remains at the logic low level. For example, from time t₅ and time t₆, the voltage 426, becomes smaller than the corresponding maximum magnitude that the voltage 426 _(i) reaches at time t₅. In another example, at time t₆, the voltage 426 _(i) becomes smaller than V+ΔV₂, even though the voltage 426 _(i) is still larger than V_(B), where V_(B) represents the threshold magnitude that is stored by the system controller 480 _(i), and ΔV₂ represents a predetermined threshold that is larger than zero. In yet another example, at time t₆, in response to the voltage 426 _(i) becoming smaller than V+ΔV₂, even though still larger than the threshold magnitude V_(B), the signal 434 _(i) generated by the system controller 480 _(i) becomes a modulation signal at time t₆, changing between a logic high level and a logic low level, as shown by the waveform 620.

According to one embodiment, the signal 434 _(i) is a modulation signal from time t₆ to time t₇. For example, from time t₆ to time t₇, the voltage 426 _(i) remains larger than or approximately equal to the threshold magnitude V_(B) by a closed-loop regulation, so that the voltage 426 _(i) remains larger than the magnitude V_(A) of the voltage 426 _(i) from time t₆ to time t₇, where the magnitude V_(A) of the voltage 426 _(i) corresponds to the holding current of the TRIAC dimmer 410. In another example, from time t₆ to time t₇, the current flowing through the TRIAC dimmer 410 remains larger than the holding current of the TRIAC dimmer 410, so that the TRIAC dimmer 410 is not turned off by the insufficient current flowing through the TRIAC dimmer 410.

According to another embodiment, time t₇ is the end of the half cycle of the AC input voltage 414 that starts at time t_(s), and time t₇ is also the beginning of another half cycle of the AC input voltage 414. For example, as shown by the waveform 610, the voltage 424 _(i) becomes zero at time t₇ and remains to be zero until the TRIAC dimmer 410 is turned on. In another example, as shown by the waveform 620, the signal 434 _(i) is at the logic high level at time t₇, and remains at the logic high level until sometime after the TRIAC dimmer 410 is turned on. In yet another example, as shown by the waveform 630, the signal 436 _(i) is at the logic low level at time t₇, and remains at the logic low level until the TRIAC dimmer 410 is turned on. In yet another example, as shown by the waveform 640, the voltage 426 _(i) decreases to zero soon after time t₇, and remains to be zero until the TRIAC dimmer 410 is turned on.

FIG. 9 is a simplified diagram of a lighting system that includes multiple lamp subsystems according to another embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. The lighting system 900 includes a TRIAC dimmer 410 and multiple lamp subsystems 910 ₁, 910 ₂, . . . 910 _(i), . . . and 910 _(N), wherein N is an integer that is larger than 1, and i is an integer that is larger than or equal to 1 and is smaller than or equal to N.

In one embodiment, each of the multiple lamp subsystems includes a rectifier (e.g., a rectifier 420), a current sink (e.g., a current sink 430), an LED driver (e.g., an LED driver 440), one or more LEDs (e.g., one or more LEDs 450), resistors (e.g., resistors 470, 472, 474, 476, and 478), and a system controller (e.g., a system controller 480). For example, the system controller (e.g., the system controller 480) of each of the multiple lamp subsystems includes terminals (e.g., terminals 482, 484, 486, and 488), and processing components (e.g., processing components 492, 494, 496, and 498). In another embodiment, the lamp subsystem 910 _(i) includes a rectifier 420 _(i), a current sink 430 _(i), an LED driver 440 _(i), one or more LEDs 450 _(i), resistors 470 _(i), 472 _(i), 474 _(i), 476, and 478, and a system controller 480 _(i). For example, the system controller 480 _(i) includes terminals 482 _(i), 484 _(i), 486 _(i), and 488 _(i), and processing components 492 _(i), 494 _(i), 496 _(i), and 498 _(i). In another example, the system controller 480 _(i) outputs a signal 434 _(i) to the current sink 430 _(i) to control the current 432 _(i). In yet another example, the current 432 _(i) is smaller than or equal to a current 920 _(i) that flows into the lamp subsystem 910 _(i). In yet another embodiment, a current 960 is equal to the current flowing through the TRIAC dimmer 410, and is also equal to the sum of a current 920 ₁, a current 920 ₂, . . . , a current 920 _(i), . . . and a current 920 _(N). For example, the currents 920 ₁, 920 ₂, . . . , 920 _(i), . . . and 920 _(N) are currents that flow into the lamp subsystems 910 ₁, 910 ₂, . . . 910 _(i), . . . and 910 _(N), respectively.

According to one embodiment, after the processing component 492 _(i) has detected that the TRIAC dimmer 410 is included in the lighting system 900, and after the processing component 492 _(i) has also determined whether the TRIAC dimmer 410 is a leading-edge TRIAC dimmer or a trailing-edge TRIAC dimmer, the processing component 498 _(i) is configured to work with the processing component 494 _(i) of the same lamp subsystem 910 _(i) and with the processing components 498 _(j) of each of the other lamp subsystems 910 _(j) to detect the holding current of the TRIAC dimmer 410, and use the closed-loop control to control the current 432 _(i), wherein j is an integer that is larger than or equal to 1 and is smaller than or equal to N, and j is not equal to i. For example, the multiple lamp subsystems 910 ₁, 910 ₂, . . . 910 _(i), . . . and 910 _(N) work together, and satisfy the following equation:

$\begin{matrix} {I_{holding} < {\sum\limits_{i = 1}^{N}\; I_{i}} < {I_{holding} \times N}} & \left( {{Equation}\mspace{14mu} 2} \right) \end{matrix}$ wherein I_(holding) represents the magnitude of the holding current of the TRIAC dimmer 410, and I_(i) represents the magnitude of the current 920 _(i). N is an integer that is larger than 1, and i is an integer that is larger than or equal to 1 and is smaller than or equal to N.

According to certain embodiments, systems and methods are provided for intelligent control related to TRIAC dimmers. For example, the systems and methods can intelligently detect the type of a TRIAC dimmer. In another example, the type of the TRIAC dimmer can be a leading-edge TRIAC dimmer, a trailing-edge TRIAC dimmer, or the situation that no TRIAC dimmer is included in the lighting system. In yet another example, the detection of the type of a TRIAC dimmer takes into account a threshold voltage as well as rate of voltage change. In yet another example, the systems and methods also provide intelligent control that matches with the detected type of the TRIAC dimmer.

According to some embodiments of the present invention, systems and methods can provide intelligent detection of the type of a TRIAC dimmer and also provide dimming control without causing one or more LEDs to flicker. For example, the systems and methods are configured to detect whether or not a TRIAC dimmer is included in the lighting system, and if the TRIAC dimmer is detected to be included in the lighting system, whether the TRIAC dimmer is a leading-edge TRIAC dimmer or a trailing-edge TRIAC dimmer. In another example, the systems and methods are further configured to detect the holding current of the TRIAC dimmer, and use the closed-loop control so that the current flowing through the TRIAC dimmer exceeds, but does not exceed too much, the holding current of the TRIAC dimmer in order to reduce flickering of the one or more LEDs and also to improve efficiency of the lighting system. In yet another example, the systems and methods are further configured to process a voltage that has waveforms not symmetric between a positive half cycle and a negative half cycle of an AC input voltage in order to provide to one or more LEDs a current that is symmetric between the positive half cycle and the negative half cycle of the AC input voltage 414. In yet another example, the systems and methods are further configured to, if the lighting system includes multiple lamp subsystems, control the current flowing through the TRIAC dimmer so that this current exceeds, but does not exceed too much, the holding current of the TRIAC dimmer in order to reduce flickering of the one or more LEDs and also to improve efficiency of the lighting system.

According to another embodiment, a system controller for a lighting system includes a first controller terminal configured to receive a first signal, and a second controller terminal configured to output a second signal to a diver component. The driver component is configured to receive a first current and provide one or more drive currents to one or more light emitting diodes in response to the second signal. Additionally, the system controller is configured to process information associated with the first signal, determine a first time period for the first signal to increase from a first threshold to a second threshold, and determine a second time period for the first signal to decrease from the second threshold to the first threshold. Moreover, the system controller is further configured to, in response to the second time period minus the first time period being larger than a predetermined positive value, determine the first signal to be associate with a leading-edge TRIAC dimmer, and in response to the first time period minus the second time period being larger than the predetermined positive value, determine the first signal to be associate with a trailing-edge TRIAC dimmer. Also, the system controller is further configured to, in response to an absolute value of the first time period minus the second time period being smaller than the predetermined positive value, determine the first signal not to be associated with any TRIAC dimmer. For example, the system controller is implemented according to at least FIG. 4, FIG. 5, FIG. 8, and/or FIG. 9.

According to another embodiment, a system controller for a lighting system includes a first controller terminal configured to receive a first signal associated with a TRIAC dimmer, and a second controller terminal configured to output a second signal to a current sink. The current sink is configured to receive a first current in response to the second signal. Additionally, the system controller includes a third controller terminal configured to output a third signal to a driver component. The driver component is configured to receive a second current and provide one or more drive currents to one or more light emitting diodes in response to the third signal. Moreover, the system controller includes a fourth controller terminal configured to receive a fourth signal. The fourth signal is related to a third current that flows through the TRIAC dimmer. Also, the system controller is configured to process information associated with the first signal, and determine the TRIAC dimmer is turned on at a first time based at least in part on the first signal. Additionally, the system controller is configured to, after the first time, with a first delay, decrease a duty cycle of the second signal from a first predetermined value until the fourth signal indicates that the TRIAC dimmer is turned off at a second time, and in response to the fourth signal indicating that the TRIAC dimmer is turned off at the second time, set a first threshold for the fourth signal, the first threshold being related to a holding current of the TRIAC dimmer. Moreover, the system controller is further configured to process information associated with the first signal, and determine the TRIAC dimmer is turned on at a third time based at least in part on the first signal. Also, the system controller is further configured to, after the third time, with a second delay, change the second signal from a first logic level to a second logic level and keep the second signal at the second logic level until a fourth time, and at the fourth time, change the second signal to a modulation signal to regulate the fourth signal at a second threshold in order to keep the fourth signal larger than the first threshold and keep the third current larger than the holding current of the TRIAC dimmer. The second threshold is larger than the first threshold, and the modulation signal changes between the first logic level and the second logic level. For example, the system controller is implemented according to at least FIG. 4, FIG. 6, FIG. 8, and/or FIG. 9.

According to yet another embodiment, a method for a lighting system includes receiving a first signal, processing information associated with the first signal, determining a first time period for the first signal to increase from a first threshold to a second threshold, determining a second time period for the first signal to decrease from the second threshold to the first threshold, and processing information associated with the first time period and the second time period. Additionally, the method includes, in response to the second time period minus the first time period being larger than a predetermined positive value, determining the first signal to be associate with a leading-edge TRIAC dimmer, and in response to the first time period minus the second time period being larger than the predetermined positive value, determining the first signal to be associate with a trailing-edge TRIAC dimmer. Moreover, the method includes, in response to an absolute value of the first time period minus the second time period being smaller than the predetermined positive value, determining the first signal not to be associated with any TRIAC dimmer. For example, the method is implemented according to at least FIG. 4, FIG. 5, FIG. 8, and/or FIG. 9.

According to yet another embodiment, a method for a lighting system includes receiving a first signal associated with a TRIAC dimmer, receiving a second signal related to a first current that flows through the TRIAC dimmer, processing information associated with the first signal, and determining the TRIAC dimmer is turned on at a first time based at least in part on the first signal. Additionally, the method includes, after the first time, with a first delay, decreasing a duty cycle of a third signal from a first predetermined value until the second signal indicates that the TRIAC dimmer is turned off at a second time, and setting a first threshold for the second signal in response to the second signal indicating that the TRIAC dimmer is turned off at the second time, the first threshold being related to a holding current of the TRIAC dimmer. Moreover, the method includes determining that the TRIAC dimmer is turned on at a third time based at least in part on the first signal, and after the third time, with a second delay, changing the third signal from a first logic level to a second logic level and keep the third signal at the second logic level until a fourth time. Also, the method includes at the fourth time, changing the third signal to a modulation signal to regulate the second signal at a second threshold in order to keep the second signal larger than the first threshold and keep the first current larger than the holding current of the TRIAC dimmer. The second threshold is larger than the first threshold, and the modulation signal changes between the first logic level and the second logic level. For example, the method is implemented according to at least FIG. 4, FIG. 6, FIG. 8, and/or FIG. 9.

For example, some or all components of various embodiments of the present invention each are, individually and/or in combination with at least another component, implemented using one or more software components, one or more hardware components, and/or one or more combinations of software and hardware components. In another example, some or all components of various embodiments of the present invention each are, individually and/or in combination with at least another component, implemented in one or more circuits, such as one or more analog circuits and/or one or more digital circuits. In yet another example, various embodiments and/or examples of the present invention can be combined.

Although specific embodiments of the present invention have been described, it will be understood by those of skill in the art that there are other embodiments that are equivalent to the described embodiments. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrated embodiments, but only by the scope of the appended claims. 

What is claimed is:
 1. A system controller for a lighting system, the system controller comprising: a first controller terminal configured to receive a first signal; a second controller terminal configured to output a second signal to a diver component, the driver component being configured to receive a first current and provide one or more drive currents to one or more light emitting diodes in response to the second signal; a third controller terminal configured to output a third signal to a current sink, the current sink being configured to receive a second current in response to the third signal; and a fourth controller terminal configured to receive a fourth signal, the fourth signal being related to a third current that flows through a leading-edge TRIAC dimmer or a trailing-edge TRIAC dimmer; wherein the system controller is configured to: process information associated with the first signal; determine a first time period for the first signal to increase from a first threshold to a second threshold; and determine a second time period for the first signal to decrease from the second threshold to the first threshold; wherein the system controller is further configured to: in response to the second time period minus the first time period being larger than a predetermined positive value, determine the first signal to be associate with the leading-edge TRIAC dimmer; in response to the first time period minus the second time period being larger than the predetermined positive value, determine the first signal to be associate with the trailing-edge TRIAC dimmer; and in response to an absolute value of the first time period minus the second time period being smaller than the predetermined positive value, determine the first signal not to be associated with any TRIAC dimmer.
 2. The system controller of claim 1 wherein the fourth signal represents the third current that flows through the leading-edge TRIAC dimmer or the trailing-edge TRIAC dimmer.
 3. The system controller of claim 1 wherein the fourth signal represents one component of multiple components of the third current that flows through the leading-edge TRIAC dimmer or the trailing-edge TRIAC dimmer.
 4. A system controller for a lighting system, the system controller comprising: a first controller terminal configured to receive a first signal associated with a TRIAC dimmer; a second controller terminal configured to output a second signal to a current sink, the current sink being configured to receive a first current in response to the second signal; a third controller terminal configured to output a third signal to a driver component, the driver component being configured to receive a second current and provide one or more drive currents to one or more light emitting diodes in response to the third signal; and a fourth controller terminal configured to receive a fourth signal, the fourth signal being related to a third current that flows through the TRIAC dimmer; wherein the system controller is configured to: process information associated with the first signal; determine the TRIAC dimmer is turned on at a first time based at least in part on the first signal; after the first time, with a first delay, decrease a duty cycle of the second signal from a first predetermined value until the fourth signal indicates that the TRIAC dimmer is turned off at a second time; and in response to the fourth signal indicating that the TRIAC dimmer is turned off at the second time, set a first threshold for the fourth signal, the first threshold being related to a holding current of the TRIAC dimmer; wherein the system controller is further configured to: process information associated with the first signal; determine the TRIAC dimmer is turned on at a third time based at least in part on the first signal; after the third time, with a second delay, change the second signal from a first logic level to a second logic level and keep the second signal at the second logic level until a fourth time; and at the fourth time, change the second signal to a modulation signal to regulate the fourth signal at a second threshold in order to keep the fourth signal larger than the first threshold and keep the third current larger than the holding current of the TRIAC dimmer; wherein: the second threshold is larger than the first threshold; and the modulation signal changes between the first logic level and the second logic level.
 5. The system controller of claim 4 wherein: the fourth signal represents the third current that flows through the TRIAC dimmer; and the first threshold corresponds to the holding current of the TRIAC dimmer.
 6. The system controller of claim 4 wherein: the fourth signal represents one component of multiple components of the third current that flows through the TRIAC dimmer; and the first threshold corresponds to the one component of the multiple components of the holding current of the TRIAC dimmer.
 7. The system controller of claim 4 is further configured to keep the third signal at the second logic level from the first time to the third time.
 8. The system controller of claim 7 wherein, in response to the third signal being kept at the second logic level from the first time to the third time, the one or more drive currents are equal to zero from the first time to the third time; and the second current is also equal to zero from the first time to the third time.
 9. The system controller of claim 4 wherein: the first logic level is a logic high level; and the second logic level is a logic low level.
 10. The system controller of claim 4 is further configured to: detect an abrupt change of slope at which the fourth signal decreases; and set the first threshold for the fourth signal based at least in part on the detected abrupt change of slope.
 11. The system controller of claim 4 wherein: the first signal includes a first pulse associated with a first input period and a second pulse associated with a second input period; and the third signal is associated with a first modulation period for the first input period and a second modulation period for the second input period; wherein the system controller is further configured to: determine the first modulation period for the first input period; change the third signal between the first logic level and the second logic level at a modulation frequency during the first modulation period; determine the second modulation period for the second input period; and change the third signal between the first logic level and the second logic level at the modulation frequency during the second modulation period; wherein: the first pulse corresponds to a first pulse width; the second pulse corresponds to a second pulse width; the first modulation period corresponds to a first duration; and the second modulation period corresponds to a second duration; wherein: the first pulse width and the second pulse width are different in magnitude; and the first duration and the second duration are equal in magnitude.
 12. The system controller of claim 4 is further configured to: process information associated with the first signal; determine a first time period for the first signal to increase from a third threshold to a fourth threshold; and determine a second time period for the first signal to decrease from the fourth threshold to the third threshold; wherein the system controller is further configured to: in response to the second time period minus the first time period being larger than a second predetermined value, determine the TRIAC dimmer to be a leading-edge TRIAC dimmer; and in response to the first time period minus the second time period being larger than the second predetermined value, determine the TRIAC dimmer to be a trailing-edge TRIAC dimmer; wherein the second predetermined value is larger than zero.
 13. The system controller of claim 4 is further configured to: during the first delay from the first time to a fifth time, keep the duty cycle of the second signal at the first predetermined value; and at the fifth time, start decreasing the duty cycle of the second signal from the first predetermined value; wherein the fifth time is after the first time but before the second time.
 14. A method for a lighting system, the method comprising: receiving a first signal; processing information associated with the first signal; determining a first time period for the first signal to increase from a first threshold to a second threshold; determining a second time period for the first signal to decrease from the second threshold to the first threshold; processing information associated with the first time period and the second time period; in response to the second time period minus the first time period being larger than a predetermined positive value, determining the first signal to be associate with a leading-edge TRIAC dimmer; in response to the first time period minus the second time period being larger than the predetermined positive value, determining the first signal to be associate with a trailing-edge TRIAC dimmer; in response to an absolute value of the first time period minus the second time period being smaller than the predetermined positive value, determining the first signal not to be associated with any TRIAC dimmer; and receiving a second signal, the second signal being related to a current that flows through the leading-edge TRIAC dimmer or the trailing-edge TRIAC dimmer.
 15. The method of claim 14 wherein the second signal represents the current that flows through the leading-edge TRIAC dimmer or the trailing-edge TRIAC dimmer.
 16. The method of claim 14 wherein the second signal represents one component of multiple components of the current that flows through the leading-edge TRIAC dimmer or the trailing-edge TRIAC dimmer.
 17. A method for a lighting system, the method comprising: receiving a first signal associated with a TRIAC dimmer; receiving a second signal related to a first current that flows through the TRIAC dimmer; processing information associated with the first signal; determining the TRIAC dimmer is turned on at a first time based at least in part on the first signal; after the first time, with a first delay, decreasing a duty cycle of a third signal from a first predetermined value until the second signal indicates that the TRIAC dimmer is turned off at a second time; setting a first threshold for the second signal in response to the second signal indicating that the TRIAC dimmer is turned off at the second time, the first threshold being related to a holding current of the TRIAC dimmer; determining that the TRIAC dimmer is turned on at a third time based at least in part on the first signal; after the third time, with a second delay, changing the third signal from a first logic level to a second logic level and keep the third signal at the second logic level until a fourth time; and at the fourth time, changing the third signal to a modulation signal to regulate the second signal at a second threshold in order to keep the second signal larger than the first threshold and keep the first current larger than the holding current of the TRIAC dimmer; wherein: the second threshold is larger than the first threshold; and the modulation signal changes between the first logic level and the second logic level.
 18. The method of claim 17 wherein: the second signal represents the first current that flows through the TRIAC dimmer; and the first threshold corresponds to the holding current of the TRIAC dimmer.
 19. The method of claim 17 wherein: the second signal represents one component of multiple components of the first current that flows through the TRIAC dimmer; and the first threshold corresponds to the one component of the multiple components of the holding current of the TRIAC dimmer.
 20. The method of claim 17 wherein: the first logic level is a logic high level; and the second logic level is a logic low level.
 21. The method of claim 17 wherein the setting a first threshold for the second signal in response to the second signal indicating that the TRIAC dimmer is turned off at the second time includes: detecting an abrupt change of slope at which the second signal decreases; and setting the first threshold for the second signal based at least in part on the detected abrupt change of slope.
 22. The method of claim 17, and further comprising: outputting the third signal; and outputting a fourth signal; wherein: the first signal includes a first pulse associated with a first input period and a second pulse associated with a second input period; and the fourth signal is associated with a first modulation period for the first input period and a second modulation period for the second input period.
 23. The method of claim 22, and further comprising: determining the first modulation period for the first input period; changing the fourth signal between the first logic level and the second logic level at a modulation frequency during the first modulation period; determining the second modulation period for the second input period; and changing the fourth signal between the first logic level and the second logic level at the modulation frequency during the second modulation period; wherein: the first pulse corresponds to a first pulse width; the second pulse corresponds to a second pulse width; the first modulation period corresponds to a first duration; and the second modulation period corresponds to a second duration; wherein: the first pulse width and the second pulse width are different in magnitude; and the first duration and the second duration are equal in magnitude.
 24. The method of claim 17, and further comprising: determining a first time period for the first signal to increase from a third threshold to a fourth threshold; determining a second time period for the first signal to decrease from the fourth threshold to the third threshold; in response to the second time period minus the first time period being larger than a second predetermined value, determining the TRIAC dimmer to be a leading-edge TRIAC dimmer; and in response to the first time period minus the second time period being larger than the second predetermined value, determining the TRIAC dimmer to be a trailing-edge TRIAC dimmer; wherein the second predetermined value is larger than zero.
 25. The method of claim 17, and further comprising: during the first delay from the first time to a fifth time, keep the duty cycle of the third signal at the first predetermined value; and at the fifth time, start decreasing the duty cycle of the third signal from the first predetermined value; wherein the fifth time is after the first time but before the second time. 